A short life and tragic death
Greatjaw had enormous, curling horns, slightly smaller than Grimgnash's but still quite impressive. That, along with his good leadership qualities and elder status, prompted King Thrasher to choose Greatjaw over Grimgnash to lead the tunneling dragons after he had died.
This infuriated Grimgnash. One night, while Greatjaw slept soundly, Grimgnash put dragonbane, a poison uniquely deadly to dragons, into Greatjaw's evening wine and awoke his brother. He appealed to him to drink the wine as an act of brotherhood and as congratulations for inheriting the throne. The tired, groggy Greatjaw drank deeply from the cup and fell back asleep. An hour later his body was seized with terrible jerking spasms and he died soon afterward.